1. Field of the Invention
The present invention relates to a method and apparatus of fabricating a thin film transistor, and more particularly, to a method and apparatus of fabricating a thin film transistor, which patterns an ohmic contact layer by a laser patterning process so that it is capable of preventing a semiconductor layer from being damaged, and reducing fabrication time.
2. Discussion of the Related Art
Generally, a thin film transistor (hereinafter, referred to as “TFT”) may be used as a switching device for controlling an operation of each pixel in a flat type display device such as a liquid crystal display device or a light-emitting display device; or may be used as a driving device for driving each pixel in the flat type display device.
The TFT includes a gate electrode, a semiconductor layer formed to be insulated from the gate electrode, source and drain electrodes formed to have a channel region on the semiconductor layer, and a pixel electrode formed to be electrically connected with the source or drain electrode.
In order to improve an electrical conductivity between a semiconductor layer pattern (a-Si) and source/drain electrodes for a related art process of fabricating TFT, an ohmic contact layer (n+ a-Si) is additionally formed between the semiconductor layer pattern and the source/drain electrodes. In this case, if the ohmic contact layer is connected between the source and drain electrodes, the ohmic contact layer functions as a conductor, whereby the TFT is not driven. For the related art process of fabricating TFT, the ohmic contact layer positioned between the source and drain electrodes (which corresponds to a channel region of the TFT) is removed by a dry etching process after patterning the source and drain electrodes through a wet etching process. During the dry etching process, the source and drain electrodes serve as a mask for etching the ohmic contact layer.
However, the related art method of fabricating TFT has the following disadvantages.
Since the ohmic contact layer is selectively etched by the dry etching process, an inaccurate etching for the ohmic contact layer may cause a problem of over etching, whereby the semiconductor layer may be damaged due to the over etching.
Also, the damage to the semiconductor layer may lower the yield of TFT.
As the ohmic contact layer is selectively etched by the dry etching process, the increased fabrication time causes deterioration of productivity.
Since the pixel electrode is electrically connected with the source electrode by photolithography, the fabrication process is complicated and the fabrication time is increased, thereby lowering the yield.